The fruitfly Drosophila is excellently suited to study the quantitative interrelation between various types of genetic damage. The wealth of refined techniques, strains, and marker combinations permit the simultaneous detection of gene mutations, small deletions, and various types of gross stuctural chromosome abnormalities. It is proposed, therefore, to undertake a systematic study of the frequencies with different categories of genetic damage are induced in a variety of different germ cell stages by representatives of both directly and indirectly acting mutagens under modifying conditions, such as storage. In addition, it is proposed to investigate in model populations the induction of genetic damage at physiologically relevant concentrations after chronic application verus short-term exposure. The proposed project is futher aimed at (1) establishing the extent to which precarcinogens can be detected as mutagens in Drosophila; (2) exploring the status of activating enzymes in successive stages of Drosophila development; (3) developing mutagen-sensitive strains for a better identification of those precarcinogens which are difficult to identify in commonly used wild-type strains; (4) analyzing the underlying causes of cases of very pronounced mutagen-specificity; and (5) clarifying whether in the absence of gross structural aberrations small deletions can be induced. It is expected that the data collected will provide a sound basis on which to evaluate the reliability of different genetic end points currently employed in the field of environmental mutagenesis. It is also hoped that the data obtained will indicate relevant problems which need to be studied in depth in the more labour-consuming mammalian systems.